It is known that corrugated filter structures are used, among other purposes, in the manufacture of filter cartridges, generally of a cylindrical shape, to filter fluids such as air, oil and gasoline which circulate inside internal combustion engines, notably for automotive vehicles.
In order to simplify the following description, and, of course, without limiting the scope of the invention, it will be assumed that, in the machines under consideration, a strip of filtering material is fed from a reel having a horizontal axis and runs with the direction of its width practically horizontal, specifically being guided or rolled at least partially on rollers having a horizontal axis. However, it will be understood that a strip may also run vertically.
More specifically, among the machines of the type mentioned above, the invention covers those that include two parallel rollers marking the axes, placed on either side of the passage of the strip, respectively, and driven synchronously in order to mark on both sides of the strip impressions marking the ridges of the ribs and the folds of the corrugated structure. Each roller is fitted with first and second sets of projecting marking lines corresponding, respectively, to the ridges of the ribs and to the folds in the sides of such ribs or cavities. A guide passage, limited on its sides by two walls, converges toward its outlet and means are provided to propel the structure to be folded through the passage at a constant speed.
In the known methods of construction of these machines, the general direction of the folded ribs was transversal, that is, perpendicular to the general direction of passage of the strip through the machine, and the folding was achieved basically by means of combs, blades, wedges or other forming elements subjected to alternating motions and acting upon the two sides of the strip in turn at the place where it enters into the guide passage. Such methods of construction ensure continuous manufacturing and present a certain number of advantages.